This photo provided by the Sacramento Police Department shows, Ka Yang, 29, of Sacramento, Calif. Yang is being held without bail in Sacramento County Jail after an investigation found her baby likely died from burns suffered in a microwave oven. Photo: AP

SACRAMENTO, Calif. — Sacramento police arrested a 29-year-old mother Tuesday after an investigation found her baby likely died from burns suffered in a microwave oven.

Ka Yang was being held without bail in Sacramento County Jail on suspicion of murder and assault resulting in the death of a child.

She was arrested three months after her otherwise healthy 6-week-old daughter, Mirabelle Thao-Lo, was found dead in the family home on March 17.

Police described the child as suffering “extensive thermal injuries.” Officer Laura Peck said the arrest took so long because investigators had to pinpoint what they believe is the cause of death by looking for other cases involving similar injuries.

They found three in the U.S., all after children were burned in a microwave: in Dayton, Ohio; Galveston, Texas; and New Kent County, Va.

“This is rare. The injuries were obviously very unique,” Peck said. “There have been only three other documented cases in the entire country where the injuries were consistent with this case….Those children were also burned and placed in the microwave.”

She said police do not know a motive. She did not believe Yang had an attorney, and none was listed in jail records.

“We wouldn’t assess her mental condition. That will be up to the court system,” Peck said. “The bottom line is no one knows what happened in that house but her and the little baby.”

Yang has three other children, all under age 7, who were removed from the home the day their sister was found dead. They are now living with relatives.

Last month, China Arnold, of Dayton, Ohio, was sentenced to life in prison without parole for the 2005 microwave murder of her 28-day-old daughter, Paris Talley.

In 2008, Joshua Mauldin, of Galveston, Texas, was sentenced to 25 years in prison for severely burning his 2-month-old daughter in a microwave oven. The girl survived, but suffered second- and third-degree burns to her left ear, cheek, hand and shoulder. Part of her left ear had to be amputated, and she required several skin grafts.

In 2000, a Virginia woman was sentenced to five years in prison for killing her month-old son in a microwave oven. Elizabeth Renee Otte claimed she had no memory of putting her son in the microwave in 1999. Experts testified that Otte suffered from epilepsy and that her seizures were followed by blackouts.